Conducting materials are to be hopefully used for varistors, sensors, and the like, while superconducting materials are also used for coil conductive wires (which show large electrical power losses), Josephson elements or magnetic shield material, and the like, because they demonstrate zero electrical resistance, Josephson effect, and full diamagnetism characteristics and the like.
As superconducting materials, conventionally, alloys such as niobium-tin alloys (which have critical temperature 18.degree. K.), niobium-germanium alloys (which have critical temperature 23.degree. K.) and the like were commonly known. The possibility of superconducting bodies with high critical temperatures made from complex oxides such as (La.sub.1-x Ba.sub.x).sub.2 CuO.sub.4 was suggested according to Bednorz and Muller, 1987. Uchida et al confirmed in 1987 that these compounds have a high critical temperate of 30.degree. K. which had not been experienced. And then, active research has been carried out on these materials.
It was discovered by Kislo et al in 1987 that the composition of (La.sub.0.9 Sr.sub.0.1).sub.2 CuO.sub.4 has a high critical temperature of 37.degree. K. Further, professor Chu of Houston University and his colleagues discovered in 1987 high temperature complex oxide superconducting material at the high temperature of 98.degree. K., exceeding the temperature of liquid nitrogen. In particular, considerable interest has been generated in a superconducting material of a composition which can be represented by the general formula: (La.sub.1-x M.sub.x).sub.y CuO.sub.4-.delta., where M is an alkali earth metal or a mixture of such alkali earth metals; x=0 to 1, y=1.5 to 2.5; and .delta.=0 to 1; or the general formula: (N.sub.1-x M.sub.x).sub.p Cu.sub.q O.sub.7-.delta. where N is Sc, Y, or a lanthanide; M is an alkali earth metal or a mixture of such alkali earth metals, x=0 to 1, y=1.5 to 2.5, p=2.5 to 3.5, q=1.5 to 3.5, and .delta.=0 to 1.
However, this type of complex oxide material is a variety of ceramic which can only be obtained in powder form, or, as a fired body in bulk form obtained by using that powder as raw material, and, after forming under pressure, providing heat treatment at a high temperature.
For this reason, it is not possible in practice to use this material as a Josephson element, which is a high speed switching element, or as a wire rod for various types of devices, so it is necessary to obtain it in film form.